Science
Some science behind PowerCranks and cycling improvements
(for the geeks and very bored) What do we mean when we say pedaling efficiency? First, a little background science. The cells in our bodies use high energy molecules to provide the energy for all sorts of functions. The most common high energy molecule used by the cell and the one important for our discussion is named adenosine triphosphate (ATP). The cell normally gets ATP by a process called oxidation of a molecule called glucose. This process only occurs in the cell, in the mitochondria, and, for maximum efficiency, requires that both oxygen and glucose be transported to the cell for this to occur. For our purposes, the ATP interacts with muscle contractile elements to cause muscle contraction (or relaxation, yes energy is required to relax a muscle also but not much as when contracting against resistance). In this way the body converts chemical energy into mechanical energy.
There are two basic types of muscle cells, called fast twitch and slow twitch. One of the major differences between fast and slow twitch muscle fibers is the amount of contractile elements and the amount of mitochondria (where ATP is made), and the amount of ATP stored, ready for immediate use. Fast twitch fibers have lots of contractile elements and stored ATP. Because they have lots of contractile elements, they have little room for mitochondria, so have few of those. This allows them to respond quickly and strongly but not for very long. Slow twitch fibers have fewer contractile elements and stored ATP but many more mitochondria. Because they have lots of mitochondria they can sustain lower levels of contractile activity for very long periods of time. Slow twitch muscles also use energy more efficiently than fast twitch muscles. Whenever, we stress a muscle cell, it will respond with time by trying to increase the amount of contractile elements and mitochondria, depending upon the stresses it regularly undergoes. This is part of the training effect.
Whichever type of cell we are talking about, as soon as a cell uses some ATP for some function, it immediately senses a need to replace it. This is done most efficiently when the cell has the optimum concentration of oxygen, fuel, enzymes, vitamins, minerals, and water, while at the right temperature and pH. This is called aerobic energy production because it requires and uses oxygen. Maintaining these optimum conditions is called homeostasis. The purpose of blood is to deliver all of these nutrients to those cells that need it and to carry away the waste products, maintaining the optimum conditions in the cell, the homeostasis. Intermittent stressing of muscles (training) causes new blood vessels to develop in the stressed muscles until the vessels have developed to the point that such stress can be sustained, no longer being perceived as stressful. This is called aerobic training. However, if at anytime insufficient oxygen is available, despite maximum blood flow, the cell will still try to make enough ATP to meet the demand. It does so by using anaerobic (without oxygen) production pathways. Generally, the cell makes 38 ATP's per glucose molecule aerobically and 2 ATP's per glucose anaerobically. For most types of racing anaerobic production of ATP (metabolism) must be avoided at all costs, not only because it is very inefficient at producing ATP, but the end product is lactic acid. Why this is so bad is discussed below.
Most people think it is the ability of the lungs to take in oxygen that limits our ability to perform. This is wrong. If it were true, when we reached our exercise limit we would turn blue from the lack of oxygen and a fair number of us would have heart attacks. I have never seen an athlete turn blue when exercising, have you? So what really limits our performance? It is not the ability to take up oxygen, it is the inability to get rid of carbon dioxide. Let me explain.
As noted above, normally lungs take in oxygen during inhalation where it is transferred to the blood which delivers it to the tissues, where it is used to "burn" glucose for energy. The waste product of this metabolism is carbon dioxide. The blood takes this waste gas and delivers it to the lungs where it is eliminated when we exhale. So, the lungs primary function is to take in oxygen and get rid of carbon dioxide, keeping the concentrations of these compounds in the body constant.
Carbon dioxide and oxygen gasses behave very differently in the body. Oxygen is very insoluble in body fluid. If it were not for hemoglobin in the red cells of the blood our blood could not carry enough oxygen to the tissues to sustain life, let alone allow for heavy exercise. Carbon dioxide is very soluble in tissue fluid. In fact, even more CO2 is present than we would expect to see from the solubility alone since, at the normal pH of 7.4, CO2 combines with water to form carbonic acid (H2CO3) which then must come into balance with bicarbonate ions. In fact, there is about 20 times more CO2 in the body in the form of bicarbonate as carbonic acid. This is one of the major buffer systems the body uses in trying to maintain optimum pH. If it were not for the large store of bicarbonate in the body pH would fluctuate wildly and cells would only rarely operate at optimum efficiency. It is an amazing and finely tuned system that works extremely well as long as enough oxygen is delivered to the tissues and the pH is maintained.
Our breathing is primarily controlled by the amount of carbon dioxide in the blood, trying to maintain the arterial CO2 constant at 40 ppm (with a secondary control based on the pH of the blood). Cardiac output is controlled by the demands of the tissues for oxygen. Under normal aerobic circumstances, the consumption of one molecule of oxygen (O2) results in about 1 molecule of CO2 and the minute ventilation of the lungs is equal to the minute cardiac output. However, when the energy demands of the muscle exceeds the ability of the blood to provide oxygen to meet these demands, the muscle gets the energy it needs from metabolism that doesn't require oxygen, referred to as anaerobic metabolism. The waste product of anaerobic metabolism is an acid, lactic acid. When lactic acid is produced it does two bad things, it changes the local pH of the cell, interfering with optimum efficiency of the cells enzymes and it interacts with the bicarbonate buffer system (which tries to modulate the pH effect). When it interacts with the bicarbonate system it releases a CO2 from these bicarbonate stores. So, we get about 38 ATP per CO2 molecule under aerobic conditions and only 2 ATP per CO2 under anaerobic conditions.
Therefore, when a muscle goes anaerobic its production of energy tries to stay the same so its production of CO2 increases about 20 times. In order to keep our muscles working efficiently we must maintain a narrow intracellular pH. When a fixed acid such as lactic acid is present, the body must compensate by reducing the amount of volatile acids (CO2) to maintain the pH. So not only does the body have to increase breathing to just keep blood CO2 within the normal limits, it must increase even more to try to reduce it below normal. (When this is done it is referred to as a compensated metabolic acidosis.) No wonder the lungs cannot get rid of this amount of extra CO2 (when it is already working near maximum). It does not take much lactic acid production to overwhelm the bodies ability to compensate, causing the intracellular pH to change, making it impossible for the muscles to maintain the current level of performance. The physiologic feature that limits our ability to exercise is not the ability to take up oxygen from the lungs but, rather, the inability to eliminate CO2 from the lungs to compensate for the production of fixed acids.
Theoretical Maximum Efficiency
If we were to burn a sugar molecule in oxygen completely in the laboratory we get CO2, H2O, and energy in the form of heat. Measuring the heat produced from this reaction is the maximum amount of energy that can be extracted from this process. The cell "burns" glucose using the oxygen in the blood in a slow, controlled chemical process, so instead of getting just CO2, H2O and heat, the cell gets CO2, H2O, a high energy molecule called ATP, and heat. The cell converts the potential energy of the sugar molecule into another high energy molecule (ATP) which the body can use to convert into mechanical energy. The ratio of the amount of mechanical energy produced to the total energy burned is muscle contractile efficiency. The maximum efficiency of this process is about 50%, i.e., half of the energy available in sugar is always converted into heat rather than useful work. This is the reason you sweat when you exercise, the body is trying to get rid of this heat. The mechanical energy that is produced, however, can then have two things happen to it. It can 1) be further directed to the rear wheel and leave as external work. or 2) be inefficiently applied and converted back into, and lost, as heat. The higher the percentage of the total energy expenditure that is transmitted to the wheel, the higher the pedaling efficiency. Experimentally measured energy efficiency of bicycle riders (including professional cyclists) ranges from about 16-22%, which is only about 30-40% of the theoretical maximum possible 50%. This leaves a lot of room for improvement, even amongst the professionals.
What Training Does
As soon as a body sees a stress beyond what it is used to it will begin adaptation to be better prepared to respond to similar stresses in the future. If the stress is not regularly repeated this adaptation will not eventually occur, but if the stress is regularly repeated, the body will eventually adapt. So, when we train the cells adapt to improve aerobic muscle functioning by increasing the concentration of the necessary cell proteins (including the number of mitochondria and contractile elements, meaning we get stronger and develop more endurance capability) and improving the ability of the body to provide oxygen and sugar to the cell by developing improved heart function and blood flow to the muscle (necessary for improved endurance). The sum total of these capacities when measured is called the aerobic capacity. Training improves our aerobic capacity.
 Although training can increase the capacity of our muscles to do work, as mentioned above, the overall measured muscle energy efficiency can never be more than about 50%, even in trained individuals. Overall pedaling efficiencies of bicyclists are measured to be, generally, 16-22%. The primary accounting for this discrepancy is inefficiencies associated with the direction the muscle contractile force is applied to the pedal. We intuitively know how to improve this efficiency because we know it is better to --pedal in circles (as shown in Figure 2) as opposed to Figure 1? Isn't that why you spent good money on fancy (and sometime expensive) shoes and clipless pedals? But, even though you purchased and use toe clips or clipless pedals, so you can pedal in circles (as shown in Figure 2) studies have consistently shown that even professional cyclists pedal as shown in Figure 1, contributing negative torque during the recovery portion of the pedaling movement (from Bicycling Science, The MIT Press, 1995, p. 63). Doubters of PowerCranks™ claims consistently point to these studies as proof that figure 1 is really the most efficient method of pedaling or the pros would be pedaling as shown in figure 2. Therefore, they claim, the PowerCranks™ claims cannot be true. However, they neglect to show any evidence that anyone (pros included) are capable of learning to pedal as shown in Figure 2 without PowerCranks™ technology such that the pros are pedaling in that fashion because it is truly optimum and not because they haven't had the tools to learn how to do it better. There has to be a reason, as more and more professionals learn about PowerCranks™, they are switching to training on PowerCranks™. This argument just doesn't hold water. Especially now that scientific studies are available that show that training with PowerCranks really does increase efficiency (see Luttrell) and power (see Dixon) in trained cyclists over training with regular cranks.
So, if you could pedal as shown in Figure 2 how much more power would you have? I (Frank Day) believe it will be possible for PowerCranks™ trained cyclists to eventually achieve overall energy efficiencies of about 30-40% (about 60-80% of the theoretical maximum, there must always be some inefficiencies from internal losses). This means your power could double (Yes, double!) over what is possible using previously available techniques. Even if this potential improvement estimate is ultimately proven grossly high, even an improvement of only 10% would be huge at the elite level. Such dramatic increases, however, will probably take several years of dedicated use. Again, experimentally measured efficiencies for even the best professional cyclists only gets to about 25%. So everyone has lots of room for improvement. Only question is, how much is possible? Not, can it occur?
Why is Our Pedaling so Inefficient?-
About the time our brains had about got down the coordination to walk reasonably well without thinking about it our parents got us our first tricycle so we could start teaching the brain how to pedal without thinking about it. But, since our first tricycle, we have always pedaled using crank arms fixed 180° apart and, until we became serious about cycling as a sport, we were never even attached to the pedals. Despite these equipment deficiencies most of us tried to go as fast as possible, sometimes even racing our friends. Therefore, our nervous system learned that “proper” and “efficient” pedaling technique involves keeping a small amount of back pressure on the pedal during the recovery, in order to facilitate rapid application of power on the down stroke. This is the most efficient pedaling dynamic if one is not attached to the pedals! By age 7 or 8 your nervous system could pedal in this “most efficient” manner without thinking and you continued to reinforce this motion for many years. But, when you eventually “graduated” to clipless pedals, what did you do to teach your unconscious brain a new, more efficient and better, basic pedaling technique? Nothing I suspect! If it were possible to correct this poor pedaling dynamic by previously available training techniques the pros would have figured out how a long time ago, but they have not! So, from the point of view of your unconscious pedaling coordination, you are still pedaling like you did as a kid – your pedaling dynamic has never changed.
What determines how much Power is available to drive the bicycle?-
The amount of power that is delivered to the wheel is determined by several factors, including:
1. Pedaling efficiency (discussed above).
2. The amount of muscle mass used in the pedaling stroke.
3. The effort expended by the rider (riding easy or hard)
4. Transmission losses.
How PowerCranks™ improves pedaling efficiency is discussed above. But, PowerCranks™ also can substantially increase the amount of muscle mass involved in the pedaling stroke, increasing power even further. The major new muscle incorporated is the iliopsoas, commonly referred to the hip flexors. These are very large and strong muscles as they are the major muscles used when doing sit ups. But, they have no aerobic capacity (if you pedal at a cadence of 90 can you do 5,400 sit ups in an hour?). PowerCranks™ improve the aerobic capacity of these muscles and, with time, these muscles have the capability of developing the same aerobic abilities as your quadriceps.
What is the PowerCranks™ Solution
PowerCranks™ have solved this training problem by combining two fixes-- into one product; a patented technological innovation and, the ability to use them in your everyday training.
The technological innovation places a very strong one-way clutch between each crank arm and the crankshaft. Because of this, PowerCranks™ work exactly like regular cranks when pedaled in a complete circle but they don't work at all if you apply a little back pressure on the upstroke. If either leg ever stops pedaling in a complete circle, even briefly, you get immediate negative feedback as your pedals fall out of synch. This is a simple, but very effective, negative feedback system. Negative feedback systems have been shown to be effective in changing all sorts of unconscious behavior. While isolated pedaling systems have existed in the past, mostly as research tools and recently in an exercycle (Reebok Strength Cycle) none of these can actually be used during actual training, giving enough repetitions to actually change behavior
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Road to Beijing with PowerCranks
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